Electric expansion valve control for a refrigeration system

ABSTRACT

A refrigeration system including a condenser having a condenser inlet and a condenser outlet, a compressor fluidly connected to the condenser inlet, and an evaporator including an evaporator inlet and an evaporator outlet. The evaporator outlet is fluidly connected to the compressor. A compressor speed sensor senses an operational speed of the compressor. An electric expansion valve (EEV) is fluidly connected to the condenser outlet and the evaporator inlet. The EEV includes a valve member that is selectively positioned to establish a desired opening to pass refrigerant from the condenser to the evaporator. A controller is electrically connected to the EEV and the compressor speed sensor. The controller establishes the desired opening of the valve member based on one of a cooling mode superheat value and a heating mode super heat value, and the operational speed of the compressor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage Application of PCT Application No. PCT/US11/48554 filed Aug. 22, 2011, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

Exemplary embodiments pertain to the art of refrigeration systems and, more particularly to an electric expansion valve (EEV) control for a refrigeration system.

Conventional refrigeration systems including a compressor that compresses a refrigerant. The refrigerant is passed through a condenser in which a heat exchange occurs with a cooling medium such as an airflow. The heat exchange lowers a temperature of the refrigerant. At the lower temperature, a portion of the refrigerant changes from a vapor to a liquid. From the condenser, the refrigerant passes through an expansion valve to an evaporator. In the evaporator, another heat exchange occurs that raises a temperature of the refrigerant. At the higher temperature, the refrigerant changes back to vapor form. The refrigerant then returns to the compressor.

The expansion valve is controlled to prevent liquid refrigerant from entering the compressor. Liquid refrigerant entering the compressor causes in “slugging” or “flooding”. Slugging can result in dame to internal compressor components. Many existing systems control the flow of refrigerant through the expansion valve by sensing “superheat” or change between refrigerant temperature or equivalent pressure in the evaporator and temperature of the refrigerant exiting the evaporator. Early refrigeration systems designed the expansion valve control to have a large safety margin to ensure liquid refrigerant does not enter the compressor. With the development of electric expansion valves (EEV), the safety margin can be reduced to enhance system efficiency.

BRIEF DESCRIPTION OF THE INVENTION

Disclosed is a refrigeration system including a condenser having a condenser inlet and a condenser outlet, a compressor fluidly connected to the condenser inlet, and an evaporator including an evaporator inlet and an evaporator outlet. The evaporator outlet is fluidly connected to the compressor. A compressor speed sensor senses an operational speed of the compressor. An electric expansion valve (EEV) is fluidly connected to the condenser outlet and the evaporator inlet. The EEV includes a valve member that is selectively positioned to establish a desired opening to pass refrigerant from the condenser to the evaporator. A controller is electrically connected to the EEV and the compressor speed sensor. The controller establishes the desired opening of the valve member based on one of a cooling mode superheat value and a heating mode super heat value, and the operational speed of the compressor.

Also disclosed is a method of controlling refrigerant flow in a refrigeration system. The method includes sensing a temperature of refrigerant entering a compressor of the refrigeration system, detecting a temperature of refrigerant at an evaporator of the refrigeration system, sensing a temperature of refrigerant at a condenser of the refrigeration system, calculating one of a cooling mode superheat value and a heating mode superheat value, determining an operational speed of the compressor, and establishing a degree of opening of an electric expansion valve (EEV) based on the one of the cooling mode superheat value and the heating mode superheat value, and the operational speed of the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 depicts a schematic diagram of a refrigeration system in accordance with an exemplary embodiment;

FIG. 2 depicts a control system block diagram for controlling the refrigeration system of FIG. 1;

FIG. 3 depicts a baseline control configuration of an electric expansion valve of the refrigeration system of FIG. 1;

FIG. 4 is a graph comparing compressor speed changes with an opening sequence of the EEV in accordance with an exemplary embodiment; and

FIG. 5 is a flow chart illustrating a method of controlling the EEV in accordance with an exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

A refrigeration system in accordance with an exemplary embodiment is illustrated generally at 2 in FIG. 1. Refrigeration system 2 includes a compressor 4 having a compressor inlet (suction side) 5 and a compressor outlet (discharge side) 6. In the exemplary embodiment shown, compressor 4 takes the form of a variable speed compressor. Refrigeration system 2 is also shown to including a condenser 10 having a condenser inlet 11 and a condenser outlet 12. Condenser inlet 11 is fluidly connected to compressor outlet 6 through a first refrigerant line 15. Condenser 10 is a first heat exchange member of refrigeration system 2. Condenser 10 is fluidly connected to an evaporator 25 having an evaporator inlet 26 and an evaporator outlet 27. Evaporator 25 is a second heat exchange member of refrigeration system 2.

In the exemplary embodiment shown, condenser 10 is connected to evaporator 25 through an electric expansion valve (EEV) 30. EEV 30 includes an EEV inlet 32 and an EEV outlet 33 and a valve member 36. EEV inlet 32 is fluidly connected to condenser outlet 12 through a second refrigerant line 39. EEV outlet 33 is connected to evaporator inlet 26 through a third refrigerant line 40. A fourth refrigerant line 44 connects evaporator outlet 27 with compressor inlet 5 to establish a closed loop refrigerant system.

In further accordance with the exemplary embodiment, refrigeration system 2 includes a compressor discharge temperature sensor 60 arranged in first refrigerant line 15. Compressor discharge temperature sensor 60 senses a temperature of refrigerant passing from compressor 4. Refrigeration system 2 also includes a condenser temperature sensor 62, and an ambient temperature sensor 65. Condenser temperature sensor 62 determines a temperature of refrigerant passing though condenser 10 and ambient temperature sensor 65 senses an ambient or outside air temperature. A condenser temperature 68 detects a temperature of refrigerant passing through condenser 25 and an indoor air temperature 72 is arranged to sense indoor air temperature. Refrigeration system 2 is also shown to include a compressor suction temperature sensor 77 arranged in fourth refrigerant line 44 and a compressor speed sensor 80 arranged at compressor 4. Compressor suction temperature sensor 77 measures a temperature of refrigerant passing into inlet 5 of compressor 4 while compressor speed sensor 80 monitors a rotational speed of compressor 4. Refrigeration system 2 is also shown to include a controller 86 linked to EEV 30 and each of sensors 60, 62, 65, 68, 72, 77, and 80 as best shown in FIG. 2.

In accordance with the exemplary embodiment, controller 86 processes signals from sensors 60, 62, 65, 68, 72, 77, and 80. When in a cooling mode, controller 86 determines a cooling superheat value and a rate of change of the cooling superheat value. The cooling superheat value is defined as a difference between temperature sensed at compressor suction temperature sensor 77 and a temperature sensed at evaporator temperature sensor 68. When in a heating mode, controller 86 determines a heating superheat value and a rate of change of the heating superheat value. The heating superheat value is defined as a difference between temperature sensed at compressor suction temperature sensor 77 and a temperature sensed at condenser temperature sensor 62. Controller 86 then establishes a degree of opening of valve member 36 of EEV 30 based on either the heating superheat value and rate of change of the heating superheat value or the cooling superheat value and rate of change of the cooling superheat value depending upon the operational mode of refrigerant system 2. In addition, controller 86 includes a compressor speed control 96, a feedback control 94 and a feed forward control 99, such as shown in FIG. 3. Feed forward control 99 anticipates and cancels changes in the degree of opening of valve member 36 resulting from superheat and rate of change of superheat vales due to changes in speed of compressor 4. More specifically, controller 86 preemptively adjusts the degree of opening of valve member 36 based on compressor speed changes sensed by compressor speed sensor 80.

FIG. 4 illustrates the relationship between the opening of valve member 36 and speed changes of compressor 4. An increase in speed of compressor 4 or a positive compressor speed change value (drps) is shown at region “A”, no speed change, i.e. compressor speed value (drps) equals zero, or compressor 4 is operating at a constant speed, is shown in region “B”, and a decrease in speed of compressor 4 or a negative compressor speed value (drps) is shown in regions “C”. When the opening of valve member 36 is fixed, the superheat value (either heating or cooling) generally increases with compressor speed and vice versa. As a result, as compressor speed is increased, the superheat value tends to go up higher and higher. Given that the compressor speed changes are known, the degree of opening of valve member 36 is adjusted preemptively to compensate for any increase in superheat value due to speed changes of compressor 4. In the exemplary embodiment shown, the speed of compressor 4 is monitored every 5 sec. The increase in speed of compressor 4 leads to an increase of the degree of opening of valve member 36 to prevent the superheat values from becoming too large. When the speed of compressor 4 is decreased, similar changes in opening of valve member 36 occur. In order to guarantee that the superheat value remains positive, the degree of opening of valve member 36 is adjusted simultaneously with decreases in the speed of compressor 4. In this manner, the any increase in superheat value resulting from a decrease in the opening of valve member 36 would not lag behind any decrease in superheat values due to a decrease in compressor speed. In this manner, any potential undershoot of the superheat value is avoided.

Reference will now be made to FIG. 5 in describing a method 200 of controlling EEV 30. Initially, a desired superheat value, e.g., heating or cooling, is set in block 204. At this point, a determination is made whether the compressor speed change value (drps) is zero in block 206. If the operational speed of compressor 4 is unchanged an EEV change value (dEEV) based on a zero compressor change value (drps) is calculated in block 208 and the opening of valve member 36 is set based on feedback control 94. The opening of valve member 36 is determined by, for example, dEEV=k₁ * (SH−SH_(des))+k₂*dSH where SH is the actual Superheat value, SH_(des) is a desired superheat value and dSH is the change in superheat value. Once the opening of valve member 36 is set adjustments to the degree of opening to fine tune the system are made in block 216.

If the compressor change value (drps) is non-zero, a determination is made in block 220 whether the compressor change value (drps) has increased. If the compressor change value (drps) is negative, an EEV change value (dEEV) based on a negative change in compressor speed value (drps) is calculated and a degree of opening of valve member 36 is set in block 222. The degree of opening is established by feed forward control 99 based on, for example, dEEV(n)=k₃*drps. In this manner controller 82 determines the whether a change in opening of valve member 32 is required to preemptively account for negative changes in the operational speed of compressor 4. If changes are required, controller 82 adjusts the degree of opening of valve member 32. Once the degree of opening is set, feed forward control 99 is reset in block 223 and any fine tuning of the degree of opening is made in block 216. At this point, feedback control 94 is reset in block 223 and adjustments are made on block 216.

If the compressor change value (drps) is positive, i.e., the operational speed of compressor 4 has increased, an EEV change value (dEEV) based on an increase of compressor speed is calculated and a degree of opening of valve member 36 is set in block 224. The degree of opening is established by feed forward control 99 based on dEEV(n)=F [k₃ * drps(n)], where “F” is a floor function. In manner similar to that described above with respect to negative speed changes, controller 82 determines the whether a change in opening of valve member 32 is required to preemptively account for positive changes in the operational speed of compressor 4. If changes are required, controller 82 adjusts the degree of opening of valve member 32. Once the degree of opening is set, feed forward control 99 is reset in block 223 and any fine tuning of the degree of opening is made in block 216.

At this point it should be understood that the exemplary embodiment describes an apparatus and method that adjust refrigerant flow from a condenser to an evaporator based not only on the superheat value, but also on compressor speed. By accounting for compressor speed, the degree of opening of the EEV is fine tuned so as to enhance the overall operational efficiency of the refrigeration system.

While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. 

What is claimed is:
 1. A refrigeration system comprising: a condenser including a condenser inlet and a condenser outlet; a compressor fluidly connected to the condenser inlet; an evaporator including an evaporator inlet and an evaporator outlet, the evaporator outlet being fluidly connected to the compressor; a compressor speed sensor that senses an operational speed of the compressor; an electric expansion valve (EEV) fluidly connected to the condenser outlet and the evaporator inlet the EEV including a valve member that is selectively positioned to establish a desired opening to pass refrigerant from the condenser to the evaporator; and a controller electrically connected to the EEV and the compressor speed sensor, the controller establishing the desired opening of the valve member based on one of a cooling mode superheat value and a heating mode super heat value, and the operational speed of the compressor.
 2. The refrigeration system according to claim 1, further comprising: a first sensor that detects a temperature of refrigerant passing into the compressor; a second sensor that detects a temperate of refrigerant passing through the evaporator; and a third sensor that detects a temperature of refrigerant passing through the condenser, wherein the cooling mode superheat value comprises a difference between temperatures sensed and the first and second sensors, and the heating mode superheat values comprises a difference between the first and third sensors.
 3. A method of controlling refrigerant flow in a refrigeration system, the method comprising: sensing a temperature of refrigerant entering a compressor of the refrigeration system; detecting a temperature of refrigerant at an evaporator of the refrigeration system; sensing a temperature of refrigerant at a condenser of the refrigeration system; calculating one of a cooling mode superheat value and a heating mode superheat value; determining an operational speed of the compressor; and establishing a degree of opening of an electric expansion valve (EEV) based on the one of the cooling mode superheat value and the heating mode superheat value, and the operational speed of the compressor.
 4. The method of claim 3, wherein establishing the degree of opening of the EEV includes establishing the degree of opening based in the one of the cooling mode superheat value and the heating mode superheat value, and adjusting the degree of opening based on the operational speed of the compressor. 